The present invention relates generally to vehicle wheel alignment. The invention relates more specifically to a noncontact wheel alignment sensor and method for aligning a vehicle wheel which eliminates the need to attach an apparatus to the vehicle or to physically contact the wheel to be aligned.
The automotive industry, in recent years, has become increasingly interested in improving the quality of its vehicles, while at the same time seeking more efficient manufacturing procedures. One area of great potential for improvement is in verifying and adjusting wheel alignment settings.
Present day wheel alignment inspection is cumbersome and relies heavily on direct contact measuring devices to obtain a reading of whether the wheel is properly aligned. Aside from being cumbersome, conventional wheel alignment verification and adjusting techniques suffer a number of other shortcomings. These shortcomings are in part attributable to difficulty in obtaining an accurate measurement due to variations in tire and wheel size, variations in tire type, variations in vehicle weight and wheel base and variations in vehicle drive method and placement of the inspection stations. Other factors, perhaps equally important, are wear on the testing apparatus over time and distortion of the tire profile caused by the direct contact of measuring tools.
If a high quality product is to be consistently produced, such parameters as wheel alignment must be carefully monitored during the manufacturing process. Preferably the accuracy of an alignment system should equal or exceed the manufacturing specifications and should be easy to use on the assembly line. Present day alignment equipment is generally deficient in one or both of these regards.
Even after the vehicle leaves the assembly line and is placed in service, there is a need for periodic inspection and adjustment of the wheel alignment settings. Proper wheel alignment can be lost if the vehicle is involved in a collision or even through normal service on bumpy roadways. Improper wheel alignment is a major contributing factor in tire wear and should therefore be periodically checked. Ideally, when a vehicle is brought in to a dealer or service station for wheel alignment, the alignment settings should be returned to the original factory specifications. Thus the dealer or service station must also have accurate alignment equipment which is capable of meeting factory specifications.
The present invention provides an apparatus and method for measuring and effecting wheel alignment in which the position and angular orientation of the wheel, tire or other desired reference point integral with the wheel is determined without physical contact. Measurements are performed by a self-contained, intelligent machine vision camera and illumination system which includes a laser source for projecting a plane of light onto the wheel, tire or other integral part of the wheel. A solid-state television camera precisely located within the camera illumination unit or sensor module, at a perspective angle relative to the axis of the projected light plane, produces image signals representing the light pattern or contour on the surface of the wheel or tire, as viewed from such perspective angle. The invention thus provides a noncontact means for measuring wheel position with no moving parts.
Control circuitry within the sensor module (camera illumination unit) transmits the image signals in response to commands from an attached machine vision computer. The computer converts these signals into digital form and stores them as an organized array of digital values representing an analog image. The machine vision computer processes the image, using prestored calibration data or n-th order polynomial transformations and preprogrammed algorithms to compute the three-dimensional position of specific reference points on the imaged object. Multiple sensor modules, rapidly sequenced by the machine vision computer, permit essentially simultaneous measurements to be made at two or more points on each wheel or tire. With these data points, the rotational plane of the wheel can be calculated. This wheel position information can be combined with similarly measured data defining the vehicle center line or other desired references and the complete vehicle alignment geometry can be analyzed and dynamically displayed on a meter or the like to guide an operator in adjusting or setting the wheel alignment. The system provides a fast response time to the operator making the adjustment while viewing the meter, through rapidly sequenced operation and hardware assisted data point location and other techniques discussed below. Alternatively, the results of the geometric alignment analysis can be transmitted digitally to an automatic mechanism for performing the same operations. The analysis can also be used for quality control testing on an assembly line by providing an indication of any misaligned wheels and also providing a printout of each wheel's actual alignment settings, if desired.
In accordance with the inventive method of aligning a vehicle wheel, structured light is projected in a plane onto the surface of a member integral with the wheel, such as the tire. This structured light illuminates at least two contour lines on different portions of the wheel. The contour lines are then optically read using an optical sensor disposed at a viewing angle offset from the plane of the structured light and data points are collected to indicate the position of the contour lines. At least one datum point associated with each of the contour lines is located corresponding to radially equivalent points (radially equidistant from the axis of rotation of the wheel) on the surface of the wheel. For example, an annular surface of the tire closest to the light projecting laser may be selected as the position from which the points are taken. Using the individual datum points so located, the position of the wheel is determined and an indication of the wheel position relative to a desired position is given to an operator. Thereafter the wheel position may be adjusted based on the indication, in order to bring the wheel into alignment with the desired position.
For a more complete understanding of the invention and its many objects and advantages, reference may be had to the following specification and to the accompanying drawings.